Efforts to make images of objects, sceneries, views of the interior of bodies and other things appear to a viewer to have three dimensions have, in the course of development, resulted in a great number of autostereoscopic methods.
Some of these methods are based on the principle that several optical views of a scene or object recorded from different angles (“perspective views”), while displayed simultaneously, are separated by suitable means so that either eye of a viewer sees only one of these views, or several but different views, resulting in a parallax effect that makes the image appear spatial.
EP 0791847 describes an arrangement in which autostereoscopic presentations are made by means of an RGB LC display used in combination with obliquely positioned lenticulars, which, in principle, produces moiré patterns. To reduce the moiré pattern, the said publication suggests that the wavelength filters assigned to the subpixels be arranged in a different configuration. The implementation of this suggestion involves the disadvantage that alterations to tried-and-approved embodiments and manufacturing processes have to be made, which would be too expensive in view of industrial quantity production of the commonly used RGB LC displays. Moreover, the measure suggested does not eliminate the disadvantages in the case of two-dimensional presentations, so that there is no consistently high image quality when the arrangement is switched over from autostereoscopic to two-dimensional presentation. The said publication relates to an arrangement in which lenticulars are used to produce the autostereoscopic presentation.
In U.S. Pat. No. 5,936,774, autostereoscopic display is based on structured light sources, which may be structured, e.g., according to their spectral properties. These interact with lens-like optical elements, which, for each perspective view, projects a group of light concentrations generated at certain distances onto specified regions of light modulators, e.g., LC displays. With these arrangements, the unfavorable effects described above also occur.
In JP 10333090, the authors suggest the use of colored illumination and wavelength filters for the directional selection of the light coming from the perspective views. An added optical filter is intended to reduce the light volume in specified wavelength ranges. This is a two-channel method based on only two perspective views, with either of the viewer's eyes being offered one of these views. According to the publication, the width of a filter element or that of an illumination element, respectively, is approximately twice the width of a subpixel in an LC display. Inevitably, this means that conventional LC cannot be used to produce the structured illumination, because the subpixel color structure of these displays is of the RGBRGBRGB . . . type. Moreover, the periodically arranged, stripe-shaped wavelength filters inevitably produce moire fringes again. An added disadvantage is the fixed distance from the image plane specified for the viewer, which derives from the equations and functions given.
JP 8163605 also describes an arrangement using two perspective views. Each of the pixels on which the views are presented is definitely visible to only one of the viewer's eyes. For directional selection of the light coming from the pixels, stripe-shaped wavelength filters are arranged in front of a display or a stripe-shaped RGB illuminating element. Here again, the disadvantages described above occur.
According to the description in JP 8146347, directional selection is effected by means of a separate transparent-opaque barrier corresponding with a wavelength filter, the transparent areas of the barrier, or the translucent areas of the wavelength filter are either slot-shaped or circular. The arrangement also has the disadvantages described above, and the same also applies to the arrangement described in JP 8146346, which uses a two-channel method with stripe-shaped wavelength filters for assigning directions to the two perspective views.
U.S. Pat. No. 5,568,313 describes an improvement of lenticular screens for 3D display by the attachment of a kind of added barrier extending all over the rear side of the lenticular. For 3D presentation, a picture assembled from stripes is placed below. The drawback is that the greater brightness achieved by imaging through a lenticular compared to imaging through a barrier is thwarted because of the added barrier extending over the entire rear side of the lenticular.
WO 01/56526 of the present applicant describes a method of spatial display achieved by means of a wavelength filter array (in special embodiments, by means of a gray level filter array) thanks to the definition of light propagation directions for light from different pixels, so that either of the viewer's eyes predominantly sees bits of partial image information from a particular selection from the views shown.